Singapore's daily newspaper, the Straits Times (clearly a microaggression towards the LGBTQ community) has a useful photo montage page continually being updated of the Summit.
https://graphics.straitstimes.com/STI/STIMEDIA/Interactives/2018/06/trump-kim-summit/index.html

The only missile that I can think of that would fit the description of the Sea Dragon program would be a sub launched SM-6.
The Drive has an article speculating on a couple examples of what the missile could be.
Related to that article.

Could it be the barrel length adding more weight at the front?
Because I swear I've seen demonstrations in Israel of some Merkava tanks driving at about top speed (50-ish km/h it was) on dirt and still doing some really fine shooting, and the MG253 gun only really has a difference in its recoil system. In terms of weight distribution it should be about the same as the Rheinmetall L/44.

I'd expect atleast 350mm RHAe in the center if we're talking 420mm composite + 240mm solid titanium (660mm LOS).
The edges of the mantlet area could present as high a value as 400mm RHAe considering the 240-280mm RHA turret armour behind the 420mm mantlet:
PS: Went and sat in a Leopard 2A5DK today and had the opportunity to eyeball the thickness of the add on armour on the upper hull. These blocks of armour looked atleast 5cm thick, probably more. So the upper hull on the newer leopards is very strong. Also had a good 5 min in the gunners position, and I must say the gunners optics are excellent, extremely crisp (no LCD screen for the gunner in the tank I sat in though). Also noted a small joystick to the right of the gunners control handle, not sure what that was for?

Tripods aren't carried at the squad level anyway, so I don't see much of a difference here.
Speaking of Wanat, that battle is a very good example of M249s and M240s going tits up - which is why the M4s were pushed so hard in the first place. And we won Wanat, overwhelmingly.